A door assembly having a flexible door panel wound and unwound on a drum or the like to selectively block or permit access through an opening, the flexible door panel having a stiffness, a width, and a length. The door assembly further includes vertically extending side columns disposed on opposite sides of the opening, the side columns being configured to engage a marginal edge of the flexible panel to vertically guide the panel while opening or closing. Attached to a leading edge of the door panel is a bottom bar having a greater stiffness than the door panel and a narrower width than a distance between the vertical panel guide assemblies. Bottom bar guides are disposed proximate a lower portion of the opening and are configured to engage a portion of the bottom bar only when the bottom bar is located in at least a partially closed position.